A wide range of medical treatments exist that utilize “endoluminal prostheses.” As used herein, endoluminal prostheses is intended to cover medical devices that are adapted for temporary or permanent implantation within a body lumen, including both naturally occurring and artificially made lumens, such as without limitation: arteries, whether located within the coronary, mesentery, peripheral, or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes.
Accordingly, a wide assortment of endoluminal prostheses have been developed, each providing a uniquely beneficial structure to modify the mechanics of the targeted lumen wall. For example, stent prostheses are known for implantation within body lumens to provide artificial radial support to the wall tissue, which forms the various lumens within the body, and often more specifically, for implantation within the blood vessels of the body.
To provide radial support to a vessel, such as one that has been widened by a percutaneous transluminal coronary angioplasty, commonly referred to as “angioplasty,” “PTA” or “PTCA”, a stent is implanted in conjunction with the procedure. Effectively, the stent must overcome the natural tendency of the vessel walls of some patients to close back down. As such, the stent acts as a scaffolding to resist the vessels tendency to close back down. Under this procedure, the stent may be collapsed to an insertion diameter and inserted into a body lumen at a site remote from the diseased vessel. The stent may then be delivered to the desired treatment site within the affected lumen and deployed, by self-expansion or radial expansion, to its desired diameter for treatment.
In certain instances due to the stretching of the vessel wall that occurs during a PTCA procedure, the stretching and widening of the vessel to reopen the lumen and the subsequent making of the vessel patent for facilitating revascularization of the heart tissue can result in vessel injury at the treatment site. The resulting trauma to the vessel wall contributes to the extent and occurrence of restenosis of the vessel. A problem associated with stent expansion at the treatment site is that the stent may need to be over expanded in order to compensate for metallurgical recoil, which occurs in high strength stents. This over expansion can contribute to the trauma that occurs to the vessel wall.
Accordingly, a vascular stent must possess a unique set of properties so that it can travel through small and tortuous body lumens to the treatment site, as well as be expanded to no more than its working diameter to provide consummate lumen expansion and radial support subsequent to implantation. Ideally, the stent should be formed from a material that exhibits a very high modulus of elasticity, a very low yield point, a high tensile strength, a variable work hardening rate, and good fatigue resistance, and that provides flexibility to the stent for navigating the tortuous vascular anatomy. Further, a radially-expandable stent must undergo significant plastic deformation when being expanded into its deployed state, which requires a stent material to have good elongation or ductility. Finally, an ideal stent material should have a high degree of radiopacity, good corrosion resistance and biocompatibility to vascular tissue, blood and other bodily fluids. However, these requirements are often competing and/or contradictory, such that a sacrifice or trade-off between one or more properties is customarily required in choosing a stent material.
Stents are typically constructed from metal alloys that include any of stainless steel, nickel-titanium (NiTi or nitinol), cobalt-chromium (MP35N), platinum, and other suitable metals. Customarily such commercially available materials are designed for one or two properties, e.g., strength and endurance, at the sacrifice of others, e.g., formidability and/or processability. Therefore, a need exists in the art for a stent made from a customized material that possesses the right balance of mechanical properties for making the vascular stent with optimal properties.